An existing NTSC receiver design is controlled by a microcomputer with communicates with various receiver sub-systems via a data bus. A particular NTSC receiver is modified to display signals conforming to synchronizing standards other than the NTSC standard. Cost and production considerations may dictate that such a multi-standard video display be engineered for minimal changes to the basic NTSC receiver design.
The existing NTSC receiver design may include a multi function integrated circuit which provides most of the sub-sub-systems required in NTSC TV receiver. Such sub-systems include, for example, IF amplification, video demodulation, chrominance demodulation and decoding, audio demodulation, sync separation and pulse and waveform generation etc. The multiple sub-systems of the integrated circuit are controlled by a microcomputer via a data bus. Hence, to facilitate the display signals other than those conforming to the NTSC synchronizing standard the multi-standard circuit design must controllable by the existing data bus and microcomputer system. Furthermore the multi-standard design must be interfaced to the existing IC sub-sub-systems for signal extraction, and must generate compatible output signals for reinsertion into the existing receiver video and synchronizing systems. However, cost and device availability preclude the use of additional bus controllable multi-standard integrated circuits. Thus, an additional requirement of a multi-standard design is the retention of microcomputer controllability without the use of additional data bus controlled devices.